Field of the Invention
The invention relates to a device for repairing a damaged area in an underwater wall region of a container or tank, in particular in the wall region of a tank of a nuclear reactor installation such as is described, for example, in our commonly assigned U.S. Patent Application Publication US 2010/0192368 A1 and its corresponding German published patent application DE 10 2008 014 544 A1. Furthermore, the invention relates to a method for repairing such a damaged area.
The wall surfaces (side walls and bottom surface) of water-flooded tanks of a nuclear reactor installation, for example the reactor pit or the fuel assembly storage tank, are provided with a liner made of steel plates welded to one another. The welds by means of which the steel plates are welded to one another or to a substructure are vulnerable to chlorine-induced stress crack corrosion as a result of mechanical stresses which inevitably occur during welding, with the result that cracks can occur over time. In order to prevent tank water from escaping into the concrete wall through such cracks, the cracks have to be sealed. In order to ensure sufficient shielding of the maintenance staff against radioactive radiation during such a repair, the water cannot be drained, in particular in the fuel assembly storage tank which is loaded with fuel assemblies, and therefore the repair has to take place under water. However, in such a fuel element storage tank in particular the side wall regions are not easily accessible since only a narrow gap is available between the fuel assembly storage rack, located in the fuel assembly storage tank, and the side walls.
In principle, it is known, for example from the commonly assigned German patent application DE 100 26 649 A1, to close off such cracks by applying an adhesive or by adhesively bonding repair overlays onto them. For this purpose, the repair overlay was applied to the wall either manually by a diver or using a linkage system operated from the edge of the tank. However, in this way, it is not possible to repair damaged areas which are not easily accessible and are located at great depth underneath the water surface.
In order to be able to repair even areas which are not easily accessible, our US 2010/0192368 A1 and DE 10 2008 014 544 A1 propose to arrange a guide system along a side wall, at a spacing distance therefrom, which guide system is secured to the side wall using suction cups and serves to guide a carriage which can be moved in a longitudinal direction of the guide system. A displaceably mounted receptacle for a repair overlay which can be applied with an adhesive surface to the wall region which contains the damaged area is arranged on the carriage. In this known device, the carriage is moved under its own weight into an end position in which the guide system is secured to the side wall with a particularly strong adhesive force using a plurality of suction cups in order to be able to absorb the opposing force which occurs when the repair overlay is pressed on. With the known device it is possible to reach side wall regions and edge regions at the bottom surface adjoining the side wall regions which are accessible only via a narrow gap due to fixtures located inside the tank, for example the fuel assembly storage rack of a fuel assembly storage tank.
Owing to the relatively long curing time of the adhesive which is used, which amounts to at least twelve hours, using the known devices to repair extensive damaged areas, which may extend, for example, over the entire length of a vertically running weld seam, involves a large amount of expenditure in terms of time.